(a) Field of the Invention
The present invention relates to a thin film transistor (TFT) array substrate for a liquid crystal display and a method for fabricating the same and, more particularly, to a TFT array substrate that can be fabricated through simplified processing steps while ensuring good performance characteristics.
(b) Description of the Related Art
Generally, a liquid crystal display (LCD) is formed with two glass substrates, and a liquid crystal sandwiched between the substrates.
One of the substrates has a common electrode, a color filter and a black matrix, and the other substrate has pixel electrodes and thin film transistors (TFTs). The former substrate is usually called the “color filter substrate,” and the latter substrate called the “TFT array substrate.”
In a liquid crystal display, lower resistance materials such as aluminum or aluminum alloy are commonly used for wiring lines in order to prevent signal transmission delays. However, in the TFT array substrate, a transparent conductive material such as indium tin oxide (ITO) is used to form pixel electrodes or to reinforce pad portions. However, ITO shows very poor contact characteristic with respect to the aluminum-based material. In this respect, a separate material should be provided between the ITO and the aluminum-based material, and in the pad portions, the aluminum-based material should be removed to prevent corrosion thereof. This involves complicated processing steps. Furthermore, when an aluminum-based layer contacts a silicon-based semiconductor layer, the aluminum content tends to be diffused through the semiconductor layer. In order to solve such a problem, it is required that a separate layer based on other metallic material should be provided between the aluminum-based layer and the silicon-based layer. This requires a multiple-layered structure having different etching conditions.
On the other hand, the TFT array substrate is usually fabricated through photolithography based on a plurality of masks. In order to reduce the production cost, the number of masks should be reduced while obtaining the same or better performance characteristic of the device.